Spawn a child process and communicate using IPC

Use Bun.spawn() to spawn a child process. When spawning a second bun process, you can open a direct inter-process communication (IPC) channel between the two processes.

To communicate with a Node.js process, set serialization: "json" in Bun.spawn. Use process.execPath to get a path to the currently running bun executable.

parent.ts

const child = Bun.spawn(["bun", "child.ts"], {
  ipc(message) {
    /**
     * The message received from the sub process
     **/
  },
});

The parent process sends messages to the subprocess with the .send() method on the returned Subprocess instance. The ipc handler also receives the subprocess as its second argument.

parent.ts

const childProc = Bun.spawn(["bun", "child.ts"], {
  ipc(message, childProc) {
    /**
     * The message received from the sub process
     **/
    childProc.send("Respond to child");
  },
});

childProc.send("I am your father"); // The parent can send messages to the child as well

The child process sends messages to its parent with process.send() and receives messages with process.on("message"). This is the same API used for child_process.fork() in Node.js.

child.ts

process.send("Hello from child as string");
process.send({ message: "Hello from child as object" });

process.on("message", message => {
  // print message from parent
  console.log(message);
});

By default, messages are serialized with the JSC serialize API, which supports everything structuredClone supports, including strings, typed arrays, and objects. This does not support transferring ownership of objects.

child.ts

// send a string
process.send("Hello from child as string");

// send an object
process.send({ message: "Hello from child as object" });

See Child processes.